Self-hardening calcium phosphate cements (CPC), developed under a NIH grant (DE05030), have proven useful in a number of dental and medical applications for which currently available materials do not work well. Results from animal studies indicated that improvements in several key properties of CPC can significantly increase the usefulness of the cement in clinical applications. The objectives of the proposed research are to elucidate mechanisms of reactions between calcium phosphate compounds that form cements and to understand physicochemical and mechanical properties of the cements formed under different conditions. The specific aims are: 1. To study the crystallinity, solubility, and rate of dissolution of the nearly stoichiometric hydroxyapatite (OHAp) formed in different cement systems and in CPCs that harden slowly or rapidly. Additionally, to determine the mechanical properties of the cements formed under these conditions. 2. To study the degree of Ca-deficiency, crystallinity, solubility, and rate of dissolution of OHAp formed in cements that have an overall Ca/P molar ratio below 1.67, and to study the mechanical properties of these cements. 3. To study the extent and the nature of carbonate incorporation, crystallinity, solubility, and rate of dissolution of OHAp formed in different cement systems and with either sodium or potassium as the cationic component of the carbonate source. 4. To study the rate of dissolution of cements that contain varied amounts of micropores (pore size of lessor 1 mum) and micropores (pore size of 150 2 200 mum). The information obtained from the proposed should be valuable in designing CPCs with specific in vitro and in vivo properties that are best suited for different types of clinical applications.